Fuel injection systems are known from the prior art, in which the fuel for the injectors assigned to the individual cylinders is centrally provided from a fuel accumulator, also referred to as “common rail”. With diesel internal combustion engines, the fuel is compressed here to up to 1800 bar with the aid of a high pressure pump in the common rail.
Here the high pressure pumps, which are embodied for instance as radial or serial piston pumps, are highly mechanically loaded, thereby running the risk of mechanical abrasion developing in the region of the piston which reaches the injection valves by way of the fuel supply line and the fuel accumulator. Modern common rail systems are on the other hand very sensitive to dirt as a result of their very small manufacturing tolerances, e.g. the piston clearance of a common rail high pressure pump amounts to 2 to 4 μm, while the guide clearance of an injection nozzle needle is less than 2 μm.
If a high pressure sensor is arranged on the fuel distributor, there is also the risk here of metallic particles blocking the bore to the measuring surface of the sensor.
Special metallic particles, which either develop as a result of the manufacturing and assembly process or as a result of wear and abrasion of the moving components during the operating time within a common rail system, may result in failure of the system.
For this reason, common rail injection systems of this type are protected by means of various filter systems. For instance, so-called filter cartridges or sieve filters are built into the fuel supply, within the high pressure pump and upstream of the injectors. The aforementioned filters are represented and described for instance in DE 10 2006 014 035 A1. This is disadvantageous in that these filters are limited in terms of their gap size and/or sieve size (e.g. gap size 20 to 40 μm, hole diameter 50 to 80 μm); a finer filtering is not possible as a result of excessively high pressure losses and for cost reasons. Furthermore, the filter would then clog far too quickly, thereby finally resulting in the engine shutting down.
A further filter facility for a high pressure range of an accumulator injection system is known from DE 100 39 425 A1. Here the filter facility is embodied as an end closure of the high pressure pipe and is completely or partially manufactured from a magnetic material.
Laboratory examinations have proved that flow dead zone areas form in the fuel distributor, in which metallic particles preferably deposit. These are preferably embodied on the front ends of the interior and/or the fuel distributor.
If, as described for instance in DE 197 29 392 A1, an end closure of the high pressure pipe is replaced by a high pressure sensor, no magnetic end closure, as known from DE 100 39 425 A1 can be used at this point. Furthermore, the measuring bore of the high pressure sensor is in this case in an afore-described flow dead zone area. As a result, there is an increased risk of interfering with the pressure measurements as a result of dirt or even blockage of the measuring bore.